5

During my commute every morning in the bus with nothing else to do, I have a strange tendency to notice antennas on the roofs of buildings. Almost every building has a Yagi, which I've been told is for TV reception.

Another one which I see that quite many buildings (mostly larger office buildings rather than homes) have is a monopole antenna with radials. Like the one in this picture, except with a longer radiating elements:

enter image description here

Image from Wikipedia.

I'm curious, what is the purpose of this antenna? And I am familiar with the characteristics of this antenna (such as the radiation pattern, etc.) but I am curious as to what they are used for. I see them alot and they all appear to be for the same purpose as they seem to be approximately the same size (thus intended for sending/receiving on the same frequency band). It's difficult to estimate the length for distance as they are quite high but they are maybe somewhere between 4 and 6 meters.

Do they maybe have something to do with TV, telephone or Internet (seems unlikely). I have only limited experience with telecommunications engineering so if anyone knows the purpose of the antennas, if there is a probable common purpose, I would be interested to know.

EDIT: One of the buildings that has this antenna is the offices of a government agency that deals with people's pensions. Another building with this antenna is a construction company.

S. Rotos
  • 3,217
  • 2
  • 27
  • 48
  • Is this in a dense urban environment? Could be nano/femto cells for 3G/4G mobile/cell phones. – Tom Carpenter Apr 21 '17 at 19:36
  • On highways a lot of antennas are for "counting" the number of passing by cellphones – PlasmaHH Apr 21 '17 at 19:36
  • Looks like an antenna for the 4 meter band. The top pole would be about 1m, and the arms as well. The arms are angled down because that helps to give the antenna a wider frequency range. Radiation pattern would be a hemisphere. – JRE Apr 21 '17 at 20:00
  • 3
    I'd guess that antenna would be for the 150 - 174 MHz land mobile band (general two-way radio for taxis, trucking companies, and many other users.) – Peter Bennett Apr 21 '17 at 20:06
  • You do not indicate your location. They could very easily be alarm company links, fire alarm or armed response. – KalleMP Apr 29 '17 at 15:35
  • What is the estimated length of the vertical element. Frequency if unloaded is about 300/(4*L) where L= length in metres. If loaded with an inductor (not apparent here) effective length will be greater. – Russell McMahon Nov 21 '21 at 05:59

2 Answers2

1

Probably a VHF band pager antenna. They are usually on top of tall buildings.

Old_Fossil
  • 383
  • 3
  • 6
0

This is probably a VHF FM radio broadcast antenna (88-108 MHz) or antenna for an FM radio repeater (increasing coverage in dead zones etc) like this:

https://www.amazon.com/dp/B07NMG3XFC/ref=cm_sw_em_r_mt_dp_DQTDTWZ5KZXRWYED7ZWB?_encoding=UTF8&psc=1

If it is on top of government buildings it could be part of the FM emergency broadcast system.

Voltage Spike
  • 82,181
  • 41
  • 84
  • 220
Ryan B.
  • 1